There are quite a few callers of seq_open that could be simplified by
setting the ->private member via the seq_open call instead of fetching
file->private_data afterwards.
Signed-off-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
---
v2:
- Fix some copy-pastos spotted by Andreas.
- Ensure everybody hit by an example patch also gets this cover letter/introducing patch.
- Include a few fs/ examples.
I've just included a few examples of possible users of this helper,
there are many more similar cases. As a bonus, 7/8 fix a potential
NULL deref (if one believes that seq_open can actually fail).
seq_open_private would have been a better name, but that one is
already taken...
Documentation/filesystems/seq_file.txt | 9 +++++----
fs/seq_file.c | 16 ++++++++++++----
include/linux/seq_file.h | 1 +
3 files changed, 18 insertions(+), 8 deletions(-)
diff --git a/Documentation/filesystems/seq_file.txt b/Documentation/filesystems/seq_file.txt
index 9de4303201e1..68571b8275d8 100644
--- a/Documentation/filesystems/seq_file.txt
+++ b/Documentation/filesystems/seq_file.txt
@@ -234,10 +234,11 @@ Here, the call to seq_open() takes the seq_operations structure we created
before, and gets set up to iterate through the virtual file.
On a successful open, seq_open() stores the struct seq_file pointer in
-file->private_data. If you have an application where the same iterator can
-be used for more than one file, you can store an arbitrary pointer in the
-private field of the seq_file structure; that value can then be retrieved
-by the iterator functions.
+file->private_data. If you have an application where the same iterator
+can be used for more than one file, you can store an arbitrary pointer
+in the private field of the seq_file structure; that value can then be
+retrieved by the iterator functions. Using the wrapper seq_open_data()
+allows you to set the initial value for that field.
There is also a wrapper function to seq_open() called seq_open_private(). It
kmallocs a zero filled block of memory and stores a pointer to it in the
diff --git a/fs/seq_file.c b/fs/seq_file.c
index 4cc090b50cc5..c8c86660f6db 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -33,11 +33,12 @@ static void *seq_buf_alloc(unsigned long size)
}
/**
- * seq_open - initialize sequential file
+ * seq_open_data - initialize sequential file
* @file: file we initialize
* @op: method table describing the sequence
+ * @data: initial value for ->private field
*
- * seq_open() sets @file, associating it with a sequence described
+ * seq_open_data() sets @file, associating it with a sequence described
* by @op. @op->start() sets the iterator up and returns the first
* element of sequence. @op->stop() shuts it down. @op->next()
* returns the next element of sequence. @op->show() prints element
@@ -45,10 +46,10 @@ static void *seq_buf_alloc(unsigned long size)
* ERR_PTR(error). In the end of sequence they return %NULL. ->show()
* returns 0 in case of success and negative number in case of error.
* Returning SEQ_SKIP means "discard this element and move on".
- * Note: seq_open() will allocate a struct seq_file and store its
+ * Note: seq_open_data() will allocate a struct seq_file and store its
* pointer in @file->private_data. This pointer should not be modified.
*/
-int seq_open(struct file *file, const struct seq_operations *op)
+int seq_open_data(struct file *file, const struct seq_operations *op, void *data)
{
struct seq_file *p;
@@ -62,6 +63,7 @@ int seq_open(struct file *file, const struct seq_operations *op)
mutex_init(&p->lock);
p->op = op;
+ p->private = data;
// No refcounting: the lifetime of 'p' is constrained
// to the lifetime of the file.
@@ -86,6 +88,12 @@ int seq_open(struct file *file, const struct seq_operations *op)
file->f_mode &= ~FMODE_PWRITE;
return 0;
}
+EXPORT_SYMBOL(seq_open_data);
+
+int seq_open(struct file *file, const struct seq_operations *op)
+{
+ return seq_open_data(file, op, NULL);
+}
EXPORT_SYMBOL(seq_open);
static int traverse(struct seq_file *m, loff_t offset)
diff --git a/include/linux/seq_file.h b/include/linux/seq_file.h
index a121982af0f5..1142e39bfad2 100644
--- a/include/linux/seq_file.h
+++ b/include/linux/seq_file.h
@@ -107,6 +107,7 @@ void seq_pad(struct seq_file *m, char c);
char *mangle_path(char *s, const char *p, const char *esc);
int seq_open(struct file *, const struct seq_operations *);
+int seq_open_data(struct file *, const struct seq_operations *, void *);
ssize_t seq_read(struct file *, char __user *, size_t, loff_t *);
loff_t seq_lseek(struct file *, loff_t, int);
int seq_release(struct inode *, struct file *);
--
2.16.4
